Twist wrapping has been extensively used for wrapping candies by twisting one or both of film ends. Such twist wrapping films are formed of a cellophane film and a uniaxially oriented polyethylene or polyvinyl chloride film.
However, cellophane films are disfavored because the cost of production is high due to the necessity to treat toxic pollutants emitted during manufacturing thereof. Uniaxially oriented polyethylene or polyvinyl chloride films, on the other hand, have the problem of insufficient twist fixing property.
Therefore, there has been attempts to prepare polyester films having good twist wrapping properties and mechanical and chemical properties, without any environmental or food hygienic problems.
For example, Japanese Laid-open Patent Publication No. Hei 2-127022 discloses that a polyester film for twist wrapping can be prepared by melt extruding a polyester resin having an intrinsic viscosity of 0.5˜1 and a melt viscosity of more than 2,300 poise at 265° C., drawing at a ratio of 2˜150, and quenching between a first quenching roll having a temperature of 40° C.˜glass transition temperature (Tg) and a second quenching roll having a temperature of Tg˜Tg+15° C.
Further, Japanese Laid-open No. Sho 61-277422 discloses a process for preparing a polyester film having a haze of more than 6% by melt extruding a polyester copolymer manufactured from terephthalic acid and a mixture of 1,4-butanediol and polyethylene glycol of MW 106˜550 and quenching by contacting the film with a cooling drum of 50˜80° C. for more than 8 sec.
However, above processes suffer from poor processibility and the printability of the resulting film is not satisfactory. Meanwhile, Japanese Laid-open Publication No. Sho 57-102317 discloses a tubular polyester film for twist wrapping prepared by extruding a polyester resin having an intrinsic viscosity of more than 0.8 to attain a sheet and biaxially drawing the sheet at a ratio of 3˜4. Japanese Laid-open Publication No. Sho 57-66933 discloses a process for preparing a tubular polyester film having a thickness of 60 micron or less by extruding a polyester resin having an intrinsic viscosity of more than 0.72 and melt viscosity of more than 6000 poise at 265° C. through an annular die; blowing at a blow ratio more than 1; and cold drawing.
However, such tubular films also have the problems of poor processibility and unsatisfactory printability.
Japanese Laid-open Publication No. Sho 51-19049 discloses a biaxially oriented polyester film comprising 95˜30% by weight of a polyester having a melting point of above 180° C. and; 5˜70% by weight of a low molecular weight polyester having an intrinsic viscosity of 0.35 or less. However, this film easily tears during the film making process.